This machine runs funny, sometimes when the parking brake is on and the handles are out it starts to stumble. Also happens on hills at times, has anyone gone through their new procedure of getting a new mercury swiitch? You have to send them the old one back before they will give you the new one, we are on day 8 of waiting with the switch jumped to allow use of the machine. The merc switch is a shot in the dark but the shop mechanic said he tried everything else. Ideas?????